Motion compensated inter-frame coding has been widely adopted in various coding standards, such as MPEG-1/2/4 and H.261/H.263/H.264/AVC. Motion estimation and compensation as well as subsequent processing are applied to the video data on a block basis. During the compression process, coding noises may arise due to lossy operations such as quantization. The coding artifacts may become noticeable in the reconstructed video data, especially at or near block boundaries. In order to alleviate the visibility of coding artifacts, a technique called de-blocking has been used in newer coding systems such as H.264/AVC and the High Efficiency Video Coding (HEVC) system. The de-blocking process applies spatial filtering across block boundaries adaptively to smooth the large transitions at and near block boundaries due to coding noises while retaining image sharpness. In the recent HEVC development, two new in-loop processing tools, named adaptive loop filtering (ALF) and sample adaptive offset (SAO), are being adopted to process de-blocked video data, where a spatial linear 2-D filter has been used for the ALF.
In HEVC Test Model Version 3.0 (HM-3.0), the conventional ALF can be selectively turned ON or OFF for each block in a picture. In the case where the picture contains only one slice, the ALF information and non-ALF-filter common information are incorporated in the slice header. When the picture contains multiple slices, the syntax design according to HEVC incorporates the ALF information and non-ALF common information in the first slice header. Also the non-ALF common information is incorporated in all other slice headers. Consequently, the non-ALF common information in all other slice headers may be redundant. Furthermore, syntax structure according to the current HEVC may suffer long delay in case of out-of-order transmission and late arrival of the first slice. In addition, incorporation of the ALF information in the first slice is hard for parallel decoding process since each of the parallel paths will have to obtain ALF information from the first slice. Therefore, it is desirable to develop a system and associated syntax structure that allows the slices to adaptively share the non-ALF common information and the ALF information among slices.